From mboxrd@z Thu Jan 1 00:00:00 1970 From: bill4carson@gmail.com (bill4carson) Date: Wed, 01 Feb 2012 11:10:21 +0800 Subject: [PATCH 2/7] Add various hugetlb page table fix In-Reply-To: References: <1327910238-18704-1-git-send-email-bill4carson@gmail.com> <1327910238-18704-3-git-send-email-bill4carson@gmail.com> <20120131095811.GB889@n2100.arm.linux.org.uk> Message-ID: <4F28AD1D.1000106@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 2012?01?31? 20:25, Catalin Marinas wrote: > On 31 January 2012 09:58, Russell King - ARM Linux > wrote: >> On Mon, Jan 30, 2012 at 03:57:13PM +0800, bill4carson at gmail.com wrote: >>> diff --git a/arch/arm/include/asm/pgtable-2level.h b/arch/arm/include/asm/pgtable-2level.h >>> index 2317a71..062c93c 100644 >>> --- a/arch/arm/include/asm/pgtable-2level.h >>> +++ b/arch/arm/include/asm/pgtable-2level.h >>> @@ -123,6 +123,11 @@ >>> #define L_PTE_USER (_AT(pteval_t, 1)<< 8) >>> #define L_PTE_XN (_AT(pteval_t, 1)<< 9) >>> #define L_PTE_SHARED (_AT(pteval_t, 1)<< 10) /* shared(v6), coherent(xsc3) */ >>> +#ifdef CONFIG_ARM_HUGETLB_SUPPORT >>> +#define L_PTE_HUGEPAGE (_AT(pteval_t, 1)<< 11) /* mark hugepage */ >>> +#define L_PTE_HPAGE_2M (_AT(pteval_t, 1)<< 12) /* only when HUGEPAGE set */ >>> +#define L_PTE_HPAGE_16M (_AT(pteval_t, 1)<< 13) /* only when HUGEPAGE set */ >>> +#endif >> (1) How does this work when normal pages can have bit 11 set if they're an >> odd PFN? > Isn't that bit 12? > >> (2) How do we even get to PTE level when a 2 or 16MB section doesn't have >> a pte table (as the L1 entry is used for the section or supersection >> mapping) ? > We don't, that's why I think we don't even need this bit defined. > First, thanks for Russel/Catalin to take time review this patch:) a: By pte used in here, I mean linux pte. linux pte is needed by generic mm layer whether this mapping is 4K, 1MB or 16MB. b: Why L_PTE_HUGEPAGE is needed? hugetlb subsystem will call pte_page to derive the corresponding page struct from a given pte, and pte_pfn is used first to convert pte into a page frame number. This is where need to be careful. Normal page based pte upper [31:12] bits is pfn, huge page(1MB) based pte upper[31:20] is pfn, so one bit MUST distinguish normal page based pte with huge page based pte. This one bit will *only* be BIT11, one last unused PTE flag within normal page. that's why L_PTE_HUGEPAGE is defined. If L_PTE_HUGEPAGE is set, then BIT19:12 is enough to be used to mark this pte is 1MB or 16MB huge page. -- I am a slow learner but I will keep trying to fight for my dreams! --bill